The present invention relates to a disc filter sector. The disc filter sector in accordance with the present invention is especially suitable for both wood processing and mining industry.
A disc filter is an apparatus used in both wood processing and mining industry primarily for thickening materials. The filter most usually comprises a number of discs which are arranged on a horizontal shaft, and the surface of which is made liquid-permeable. The discs of the filter are arranged in a vat rotatably around their axis so that at least a half of the disc surfaces is submerged in the vat in the material to filtered. Said discs are formed of a number of so called sectors next to each other having their inner ends connected to the shaft so that the liquid that has passed the sector surface is allowed to flow from the inside of the sector through the shaft out from the apparatus. The surface of the sectors may be made either of cloth, plastics or metal wire or even of a perforated plate. If a wire is used the sector requires a special supporting structure, which keeps the flexible and elastic wire in shape. Almost an innumerable amount of different technical solutions are possible in the supporting structure of the sector. For example, the use of different wooden or plastic profiles as supporting structures is known.
Swedish patent 79654 illustrates a sector structure, which has a plate substantially undulating in V-shape, in which plate the undulations are parallel. U.S. Pat. No. 3,948,779 disclose a supporting structure for the sector, which is also undulating in V-shape, but the undulations in this arrangement are radial. WO publication 87/04640 also illustrates a sector structure having V-shaped radial undulations. Further, also published Swedish patent application 465 658 discloses a supporting structure with V-shaped undulations. It is a characterizing feature of-all above described structures that the filtering surface of the sector is supported against the ridge of the undulated plate, whereby the pressure differences between the outer and inner surface of the sector, especially at high pressures of the washing liquid, of course, tend to press the wire surface to the groove between the ridges. Moreover, the bending stiffness parallel to the rim of such an undulated sector is very weak, especially when the supporting structure is simple.
The above mentioned US and WO publications as well as U.S. Pat. No. -2781,133 also each methods of making the supporting structure of the sector rigid parallel to the rim, for example, by arranging two undulated plates opposite to each other or by attaching supporting ribs or like parallel to the rim of the undulated plates. The positioning of such supporting ribs and finding appropriate welding surfaces makes the manufacture of the sector complicated and risky.
The object of the present invention is to facilitate the manufacture of the filter sector and to simplify the structure thereof. If, for example, a sector in accordance with the present invention is manufactured by welding, the amount of the necessary welding spots diminishes at least to half of the previous- Further, an object of the present invention is to bring about a sector having a high bending stiffness. Yet another object of the present invention is to bring about a sector, which is highly supporting to the wire.
The characteristic features of a disc filter sector fulfilling the objects of the present invention become apparent in the accompanying patent claims.
Advantages of a sector of the present invention compared with the sectors in accordance with prior art are, for example, the following:
a sturdy box structure, in which separate supporting ribs inside the sector are not necessary; PA1 it supports the wire well; PA1 separate flow channels for the filtrate, i.e. a small flow resistance; PA1 the filtrate volume may be minimized allowing a possibility to optimize the whole operation of the filter apparatus; PA1 smaller need of material, lighter, easier to manufacture, less welding, minimized plate thickness compared to a conventional perforated plate sector; PA1 it is easy to arrange the "conicity" of the sector towards the inner end by means of undulations, the part closer to the shaft being thicker than the part further apart, whereby the cross-sectional flow area remains constant throughout the entire sector; PA1 90% of the through-washability remains; and PA1 the sector is formed of identical halves, which further facilitates the manufacture of the sector.